1. Field of the Invention
This invention relates to a magenta toner used in the formation of images by development of electrostatic latent image or by toner jetting. More particularly, it relates to a magenta toner that can exhibit high minuteness even with use of heat-and-pressure fixing means in which any oil for preventing high-temperature offset is not used or such an oil is used in a small quantity.
2. Related Background Art
In recent years, commonly used in full-color copying machines proposed are a method in which, using four photosensitive members and a belt-like transfer member, electrostatic latent images formed respectively on the photosensitive members are developed with a cyan toner, a magenta toner, a yellow toner and a black toner to form corresponding toner images and then a transfer medium is so transported as to be held between the photosensitive members and the belt-like transfer member to transfer the toner images thereto in straight pass, followed by fixing to form a full-color image thereon, and a method in which the transfer medium is wound around the surface of a cylindrical transfer member set opposingly to a photosensitive member, by the aid of electrostatic force or mechanical action of a gripper or the like, and the steps of development and transfer are carried out four times, followed by fixing to form a full-color image thereon.
As toners used in such full-color copying machines, the toners are required to be well color-mixed in the step of heat-and-pressure fixing, without damaging any color reproducibility and any transparency of overhead projection (OHP) images. Compared with ordinary black toners for black-and-white copying machines, toners for full-color images may preferably make use of low-molecular-weight binder resins having sharp-melt properties. However, usually, the use of such binder resins having sharp-melt properties tends to cause a problem on high-temperature anti-offset properties because of a low self-cohesive force of the binder resins when the toners melt in the step of heat-and-pressure fixing. In ordinary black toners for black-and-white copying machines, relatively highly crystalline waxes as typified by polyethylene wax and polypropylene wax are used as release agents in order to improve high-temperature anti-offset properties at the time of fixing. For example, these are disclosed in Japanese Patent Publication No. 52-3304 and No. 52-3305 and Japanese Patent Application Laid-open No. 57-52574. In the toners for full-color images, such release agents may inhibit transparency when images are projected by OHP, because of their high crystallizability and a difference in refractive index between them and materials of OHP sheets, so that the projected images may have low saturation (chroma) and lightness.
To solve such a problem, toners having a specific storage elastic modulus are proposed. For example, Japanese Patent Applications Laid-open No. 11-84716 and No. 8-54750 disclose toners having a specific storage elastic modulus at 180xc2x0 C. or 170xc2x0 C. However, as for color toners required to have both low-temperature fixing performance and high-temperature anti-offset properties, to have a good fixing performance in the heat-and-pressure fixing means in which any oil for preventing high-temperature offset is not used or such an oil is used in a small quantity, and to have a sufficient color mixing performance, the toners may have too low viscosity and also have not been satisfactory in respect of storage stability in a high-temperature environment. Japanese Patent Applications Laid-open No. 5-249735, No. 7-92737, No. 7-234542, No. 7-295298, No. 8-234480, No. 8-278662 and No. 10-171156 also disclose toners having specific storage elastic moduli. However, in order to attain fixing performance, storage stability and OHP transparency which are ideal for color toners, there has been room for improvement.
To solve the above problem, as disclosed in Japanese Patent Applications Laid-open No. 4-149559 and No. 4-107467, a method is proposed in which a nucleating agent is used in combination with a wax so as to lower the crystallizability of the wax. As also disclosed in Japanese Patent Applications Laid-open No. 4-301853 and No. 5-61238, a method is proposed in which a wax having a low crystallinity is used. As waxes having a relatively good transparency and a low melting point, montan type waxes are available. Use of montan type waxes is disclosed in Japanese Patent Applications Laid-open No. 1-185660, No. 1-185661, No. 1-185662, No. 1-185663 and No. 1-238672. These waxes, however, by no means satisfy all the transparency in OHP and the low-temperature fixing performance and high-temperature anti-offset properties at the time of heat-and-pressure fixing.
Accordingly, in usual color toners, an oil such as silicone oil or fluorine oil is applied to heat fixing rollers without adding any release agent as far as possible, so as to achieve an improvement in high-temperature anti-offset properties and OHP transparency. However, fixed images thus obtained have excess oil having adhered to their surfaces. This oil may adhere to photosensitive members to cause contamination or the oil may swell fixing rollers to shorten the lifetime of the fixing rollers. In order not to cause any oil streaks on the fixed images, it is necessary to feed oil onto the fixing roller surface evenly and in a constant quantity. This tends to require fixing assembles having a large size.
Accordingly, in the heat-and-pressure fixing means in which any oil is not used or the oil is used in a small quantity, it is long-awaited to provide a toner having kept offset from occurring and also promising superior transparency of fixed images.
Meanwhile, with an increase in instances in which color copying machines are connected to computers via controllers and used as high-grade color printers, a color management system has come to be proposed which makes color control of the whole system. As the result, specific users have come to strongly demand that the printed images produced by a color printer of an electrophotographic system are identical in tinges with the printed images produced by printing making use of process inks. Thus, there has come to be a demand for toners capable of providing the same color tones as process inks.
Some proposals have ever been made on pigments for magenta toners. In view of superior sharpness and transparency of color and also superior light-fastness, quinacridone pigments have been in wide use.
For example, Japanese Patent Applications Laid-open No. 49-27228, No. 57-54954 and No.1-142559 disclose a toner making use of 2,9-dimethdylquinacridone alone. This toner certainly has a superior light-fastness, but can not be said to be a well vivid magenta toner. Japanese Patent Application Laid-open No. 64-9466 discloses that a quinacridone pigment and a xanthene dye or a pigment obtained by making a xanthene dye into a lake are used in combination so as to improve the vividness of toners. This toner has not attained a sufficient vividness, and has had a problem that it changes in color and images formed may change in color when left over a long time.
Japanese Patent Application Laid-open No. 1-154161 discloses use of a quinacridone pigment of 0.5 xcexcm or smaller average particle diameter in an attempt to improve the transparency of magenta toners. The transparency of toners depends on pigments, resins and how and to what extent the pigments are dispersed in resins, and any magenta toners having a high transparency have not necessarily been obtained.
Meanwhile, in the case of full-color images, colors are reproduced using three chromatic toners consisting of three-primary-color coloring materials, a yellow toner, a magenta toner and a cyan toner, or four color toners consisting of these toners and a black toner added thereto. In order to obtain images having the intended color tones, the balancing of different colors is important, and it is also attempted to a little change the color tone of the magenta toner.
For example, Japanese Patent Publication No. 63-18628 discloses a mixture of compounds which contains two types of substituted quinacridones. Japanese Patent Application Laid-open No. 62-291669 discloses use of a mixed crystal of 2,9-dimethylquinacridone and unsubstituted quinacridone as a magenta colorant, which is proposed as a colorant having the intended hue and also aiming at an improvement in triboelectric charging performance of toners.
Its color tone has more shifted toward a tinge of yellow as a whole than the case of the sole use of 2,9-dimethylquinacridone. However, it tinges strongly with blue compared with the hue of magenta inks for offset printing. Thus, there have remained many points to be improved.
Japanese Patent Application Laid-open No. 2000-181144 discloses an image-recording coloring composition of vivid magenta color in which a dimethylquinacridone pigment and a red pigment are used in combination. However, according to studies made by us, there still is room for further improvement in respect of anti-offset properties at the time of continuous fixing, and the composition is not on the level satisfactory as toners for oilless fixing.
An object of the present invention is to provide a magenta toner having solved the problems discussed above.
More specifically, an object of the present invention is to provide a magenta toner having superior low-temperature fixing performance.
Another object of the present invention is to provide a magenta toner having superior storage stability, heat resistance and anti-blocking properties.
Still another object of the present invention is to provide a magenta toner which has a high coloring power that covers a broad dynamic range of from low density to high density, affords high saturation and lightness, affords superior OHP transparency, enables superior dispersion of colorants, promises a high light-fastness and also have a color tone agreeing with the magenta of process inks.
A further object of the present invention is to provide a magenta toner which can exhibit good fixing performance and color mixing performance, has a sufficient triboelectric chargeability, affords glossiness high enough to improve image quality, can well prevent high-temperature offset, has a broad fixable temperature range, has been kept from causing melt adhesion of toner to the interior of developing assembly, i.e., parts such as a sleeve, a blade and a coating roller, also shows a good cleaning performance, and has been kept from causing filming to the photosensitive member surface.
A still further object of the present invention is to provide a magenta toner which has been kept from causing fog, has a superior highlight reproducibility, promises a solid-image uniformity, and has a superior running stability.
To achieve the above objects, the present invention provides a magenta toner containing at least a binder resin and a colorant, wherein;
the magenta toner has a storage elastic modulus at a temperature of 80xc2x0 C., Gxe2x80x280, in the range of from 1xc3x97106 dN/m2 to 1xc3x97108 dN/m2 and a storage elastic modulus at a temperature of from 120xc2x0 C. to 180xc2x0 C., Gxe2x80x2120-180, in the range off 2xc3x97103 dN/m2 to 1xc3x97106 dN/m2; and
the magenta toner contains at least i) at least one compound selected from the group consisting of compounds represented by the following Formulas (1) and (2) and ii) a compound represented by the following Formula (3): 
wherein RD2 represents H or OCH3, RD4 represents H or CONH2, RD5 represents H, SO2N(C2H5)2 CONHC6H5, CONH2 or CONHC6H4-(p)CONH2, RK2 represents H, OCH3, CH3 or OC2H5, RK4 represents H, OCH3 or Cl, and RK5 represents H, OCH3, Cl or NO2; 
wherein RD2 represents H or SO3xe2x88x92, RD4 represents H, Cl or CH3, RD5 represents H, Cl, CH3, C2H5 or SO3xe2x88x92, and M represents Ba, Ca, Sr, Mn or Mg; provided that one of RD2 and RD5 is SO3xe2x88x92; 
wherein RD1, and RD2 each represent H or CH3.